1. Field of the Invention
The present invention relates to moisture-hardening binder compositions based on copolymers containing anhydride and carbonate groups and compounds containing blocked amino groups which are suitable for crosslinking the copolymers.
2. Description of the Prior Art
The use of compositions based on organic compounds containing at least two intramolecular carboxylic anhydride groups per molecule, especially copolymers containing succinic anhydride, and polyhydroxyl compounds as binders for paints and coating compositions is known from EPA-48 128. However, the possibility of applying the principle of this publication to the reaction of amines with anhydrides is complicated by the fact that the reaction of amines with anhydrides is a reaction which takes place very quickly at room temperature and which leads to crosslinked products with elimination of anhydride. The resulting extremely short pot lives have previously prevented polyanhydrides and polyamines from being used together in coating systems.
A possible solution to this problem is disclosed in DE-OS 2 853 477 which describes mixtures of blocked polyamines and polyanhydrides which have good pot lives and which harden on upon the addition of water to form crosslinked products. Ketimines or aldimines obtained by the reaction of polyamines with ketones or aldehydes are described as suitable blocked polaymines.
Compounds containing at least two cyclic carboxylic anhydride groups in the molecule, especially reaction products of polyols with cyclic dianhydrides, in which the ratio of hydroxyl to anhydride groups is 1:2, or copolymers of an unsaturated cyclic anhydride with polyunsaturated compounds or .alpha.-olefins are disclosed as suitable polyanhydrides.
The olefinically unsaturated compounds to be used in the production of the copolymers are only discussed in very broad terms in the general description of DE-OS 2 853 477. In particular, there is no disclosure of the quantities in which the individual monomers are to be used for the production of the copolymers. The examples are limited to copolymers of butadiene oil and maleic anhydride in a ratio of 1:1 and to copolymers of wood oil with maleic anhydride. However, these copolymers are attended by disadvantages because their combination with bis-ketimines or bis-aldimines results in heavily discolored products. In addition, coating compositions containing unsaturated oils, such as butadiene oil or wood oil, as the binder component lead to coatings which turn brittle very easily and are not weather-resistant.
In addition, the examples of DE-OS 2 853 477 demonstrate the use of dimethyl formamide as solvent in the processing of the binders specifically described therein at solids contents of only about 20%, which is unacceptably low.
Another possibility for increasing the pot life is to use oxazolidines instead of amines. Water-hardenable compositions of oxazolidines and polyanhydrides are disclosed in DE-OS 2 610 406 for use as water-hardenable sealing and adhesive compositions. Reaction products of polyunsaturated fatty acids with maleic anhydride and polyanhydrides of C.sub.3-6 alkyl (meth)acrylate and maleic anhydride, especially of butyl acrylate and maleic anhydride, are described as especially preferred polyanhydrides.
The systems specifically described in DE-OS 2 610 406 need considerable improvement in regard to their suitability for the production of high-quality, colorless paint films which combine extreme hardness with high resistance to solvents and chemicals. This need for improvement applies both to the systems based on copolymers of maleic anhydride and butyl acrylate described in the examples and also to the systems based on reaction products of maleic anhydride with polyunsaturated fatty acid esters which result in end products which yellow.
The use of carbonate-functional compounds in combination with polyamines for paints and coating systems is known, for example, from EP-A-1088. However, the reactivity of these binder combinations needs to be improved. When hardening is carried out at room temperature, crosslinking is either inadequate or requires very long reaction times, even in the presence of catalysts.
EP-A-286 933 describes special hardening components (A) for compounds containing epoxide or cyclic carbonate groups which are distinguished by the fact that the hardening component (A) is a reaction product of (a1) CH-active alkyl esters or adducts of CH-active alkyl esters and isocyanates with (a2) polyamines.
Accordingly, an object of the present invention is to provide new binder compositions which are suitable for the production of high-quality, optionally moisture-hardening systems having good pot lives. It is a further object of the present invention to provide binder compositions which result in coatings which are clear, colorless, non-yellowing and solvent-resistant.
These objects have been achieved in accordance with the present invention as described hereinafter. Previously unknown copolymers containing both anhydride and carbonate groups in chemically incorporated form are present as component A) in the binder compositions according to the invention. Hardening component B) is based on compounds containing blocked amino groups which are capable of activation in the presence of moisture.